Thin-film electroluminiscent display components, which are in themselves known (cf., e.g., U.S. Pat. No. 3,560,784), are in principle also suitable for large-area applications, since the thin films can be readily processed onto substrates of several square decimeters. In practice, however, problems have been encountered in attempting to produce display elements of a large area.
In this regard, all thin films and thin-film components, produced in accordance with practical manufacturing processes, embody defects such as structural defects, holes, inhomogeneities, and impurities, etc. Such defects are often detected in connection with the basic testing of the component, but some remain undetected until later when the component is subjected to various environmental and operational strains. The nature of the defects vary so that some become evident under a slight strain, while others do not become a problem until the film is subjected to a severe strain. In connection with strain tests, one also must consider the frequency of defects per unit of area, or the yield of components after the performed tests. Typical tests are voltage-endurance tests, tests at an elevated temperature, humidity tests, sevice-life tests, and accelerated service-life tests, etc.
When these same techniques are applied to large-scale thin-film display components, however, it has been noticed that a unified large area of a display element is in itself an additional strain for the whole component, in which case there is an unacceptable number of defects (i.e. the yield is lower).
Moreover, a unified large-area display element (&gt;1 cm.sup.2) also gives rise to certain drawbacks which are difficult to overcome. Specifically, due to the capacitance between opposed electrodes, energy is stored in the display element sufficient to destroy the entire element if a weak point is encountered. Also, the series resistance (the resistance of the continuous transparent conductor) to a possible defective point is low, so that the current may increase to a destructively high level on an instantaneous disruption. Along these same lines the series resistance between the power source proper and the display element does not prevent destruction (does not limit the current), because the capacitance of the display element itself supplies sufficient destructive energy. Furthermore, inhomogeneities in a large-area display element, may cause heat generation at different parts of the element. Thus, hot points may be produced, which may result in destruction of the element as a result of a so-called thermal surge.